How to Predict Everything

ANNALS OF SCIENCE about the prediction theory put forward by Princeton astrophysicist J. Richard Gott III, 52... In the seventies, he and several colleagues published an influential paper arguing that the universe is geometrically “open”--meaning that it will go on expanding forever. Then, building on research pioneered by Kip Thorne, the eminent black-hole theorist at Caltech, he identified circumstances under which time travel into the past might be possible, inside black holes. This work has held up well, and has contributed to Gott’s growing reputation as a provocateur whose ideas, although sometimes startling, are difficult to dismiss... Gott is exquisitely serious about science, and is given to long-playing discourses—he can spend forty minutes answering a question without wasting a word—but a playful irony is seldom far from the thread of his conversation.... The question that Gott has been asking lately is how long the human species is going to last. Since scientists generally make predictions at the ninety-five-per-cent confidence level, Gott begins with the assumption that you and I, having no reason to think we’ve been born in a special time, are probably living during the middle ninety-five per cent of the ultimate duration of our species. In other words, we’re probably living neither during the first two and a half per cent nor during the last two and a half per cent of all the time that human beings will have existed. “Homo sapiens has been around for two hundred thousand years,” Gott said, once we’d finished our entrees. “That’s how long our past is. Two and a half per cent is equal to one-fortieth, so the future is probably at least one-thirty-ninth as long as the past but not more than thirty-nine times the past. If we divide two hundred thousand years by thirty-nine, we get about fifty-one hundred years. If we multiply it by thirty-nine, we get 7.8 million years. So if our location in human history is not special, there’s a ninety-five-per-cent chance we’re in the middle ninety-five per cent of it. Therefore the human future is probably going to last longer than fifty-one hundred years but less than 7.8 million years. “Now, those numbers are interesting, because they give us a total longevity that’s comparable to that of other species. The predicted total lifetime of the human species is quite similar to the ranges we see for other species—species that have gone extinct. Homo erectus, our ancestor species, lasted for about 1.6 million years. The Neanderthals went extinct after about three hundred thousand years. The mean duration for all mammal species is two million years.”... Gott, after rummaging around in his attache case, produced a set of dominoes, which he set up in five stacks of doubling height, starting with one domino and ending with a stack of sixteen. “These dominoes represent the human population over time,” he said. “We’ve gone through a period of exponential growth, so I have one, two, four, eight, and then sixteen dominoes. Now, what’s going to happen in the future? One prospect is that the population will reach a peak, then go back down at a similar rate. This is something that has happened to many species: you have an exponential growth rate that reaches a peak and then something bad happens and you have an exponential decline. In that case, you would expect to be right about here, near the peak. Most people are. And that’s where we are... If the population is going to decline, then we’re living in exactly a typical place, just as one would expect.” ...This is the part of Gott’s argument that most troubles me—not because I can find fault with it but because I can’t. It ranks as one of the most baleful prognostications of the human fate since Malthus. Gott went happily on, tapping his right index finger on the domino plateau. “A lot of people say, ‘Well, our species may go out of existence, but we’ll be replaced by smarter, genetically engineered human beings. We’ll have many descendant species, so we shouldn’t mourn if Homo sapiens goes extinct, because we’ll be replaced by something much better.’ But, as Mr. Darwin noted, most species do not leave any descendants. A few do, and they leave a lot: there are sixteen species of rodents. Our genus, Homo, is down to one. We’re like the horse. There used to be several, now there’s only one. There used to be several different hominid species—the Neanderthals and us, for example—and now we’re down to one.” This is not a good sign. Describes his argument for colonizing Mars... “The manned space program is thirty-eight years old, so it’s been around only a short time,” he said. “Things that haven’t been around a very long time are not likely to be around very long in the future. So there’s a real danger that we will quit it, as the Chinese did in the fifteenth century. They explored Africa, came back with a giraffe that everybody wondered at, and then they just quit. The period of great Egyptian pyramid-building lasted about a century from the first to the biggest; then there was a long, slow decline during which the Egyptians built crummy ones. So there’s a danger that we’ll end up stuck on the earth—that if we wait too long we may have a population that’s too small to respond to an emergency or to do space colonization.”... Outside, at the curb, I waved goodbye as Gott’s car headed crosstown, bound for Princeton. That car is about a year old, I thought, so it’s likely to keep running for more than a week but less than thirty-nine more years. New York City was first settled in 1626; that gives it nine and a half to 14,500 years to go. Jupiter stood high in the southern sky, warranteed for at least another hundred and fourteen million years. Science, like art, changes the way one looks at things.

Recommended Stories

As the years passed, Tom grew more entrenched in his homelessness. He was absorbed in lofty fantasies and private missions, aware of the basest necessities and the most transcendent abstractions, and almost nothing in between.